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Tone controls

s-petersen

s-petersen

Scott
Hi Guys and Gals,
I have a Dynaco Pat 4 I would like to convert to tubes, but many of the controls (which are quiet and track well) are different resistances than the circuits I would like to try.
Is there a way to figure out which other values need to be changed in an existing circuit to make the new circuit work the same way as in the original schematic?
Some tone circuits are feedback, others are pass through(passive).
Eico HF-84,85, Bogen PR2, Fairchild 248, and possibly BTH A1A are some of the possibilities I am thinking about.I don't have any need of a phono stage, but a loudness button would be a plus.
After the Dynaco conversion, I may try a scratch built based on an Eico HF-85 chassis.

Thanks,
Scott
 
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Did you compare the SS schematic, to a Dynaco tube pre amp? You may just end up using the chassis and following a pre amp design you like... That's what I'm doing with my small guitar amp project....
 
I did compare,something wasn't the same, IIRC,I already have several pas preamps,so I know what they sound like.Possibly I can look for an aftermarket Pas line stage upgrade board for something different,I was thinking point to point might be better for what want to do. I have some Eico pec replacement boards I can also use.
 
Cool,,, I was thinking of Fisher, or one of the high end pre's of the era... It would be P2P for me, not a fan of the boards... Looking forward to what you come up with...
 
Pat 4 volume 250k balance 220k 40k treble and 50k bass.
Eico Hf-85 volume 500k treble 500k bass 1meg
Eico ST-84 volume 250k treble 500k bass 1meg Balance 750K
Fairchild 245 volume 180k treble 500K bass 500k
Bogen PR2 volume 500k treble 2meg bass 2meg
BTH A1A volume 250k treble 250k bass 250k Balance 250k
 
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Usually thats so, but on fully passive controls it might be audio taper pots for tone. Balance pots are linear taper.
 
I may end up trying to find pots to fit the knobs on the Dynaco,the values are so different.
I may end up looking for knobs to replace the concentric tone control pots with solid shaft knobs
I think I am going to try the ST 84 first. The Pat4 has most of the same controls (settings).
 
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Seasons Greetings Scott, "Best Wishes for You, Your Family, Friends and Loved Ones on this coming New Year"

Why not consider a scratch build Tube Pre with what you want before you go and tear into your PAT 4.
 
I like the way it looks,It needs rebuilding and upgrades to sound decent from what I understand. I have a Pat 5 bi fet someplace I have used in the past that I didn't really like the sound of,I don't think this would sound better even with the upgrades,I bought it from Vinyl fiend last year at the HV freezefest to try this on. For $40 it was cheap enough to experiment on.If it doesn't work out,no damaging mods will be done.
Later I will copy A HF 85 for a scratch built(with some original chassis parts thrown in.)

Have a Happy Holiday to you also. I don't know where I heard it,but Have a Happy non denominational holiday to you!
My Brother is a Jehovah witness,That is how I wish him a Happy Birthday, He laughs.

I searched,it was Larry the cable guy.
 
s-petersen said:
Is there a way to figure out which other values need to be changed in an existing circuit to make the new circuit work the same way as in the original schematic?
Click to expand...
All of the values of the RC components have to be changed because the tubes and the transistors/FETs have completely different impedances, so essentially you will be re-building/cloning a tube-based tone control from scratch. If you already have a tube preamp with tone control, then it might be easier to just change the pots to newer, better ones.
 
I knew things would have to be changed.I was looking for some kind of calculator,of formula to calculate the other values based on the pots.The more I think about it,the less I think the original tone controls could be driven by the tube versions of the schematics.Because they were concentric,I will have to find new knobs for the new tone controls.
 
S-petersen,

If you have to redesign (which is probable), keep in mind that 'linear law' stereo pots track better than 'log law', which is mostly used for passive tone controls. Linear pots find use in feedback circuits like the Baxandall.
 
jazbo8 said:
Try downloading Duncan Monroe's ToneStack Calculator if you want to design your own.
Click to expand...
Thanks! downloaded it.
Audiovet said:
S-petersen,

If you have to redesign (which is probable), keep in mind that 'linear law' stereo pots track better than 'log law', which is mostly used for passive tone controls. Linear pots find use in feedback circuits like the Baxandall.
Click to expand...
I'll try it after I build the Eico ST-84 circuit
This new site software is messin' with me! I thought I posted,but I didn't hit "post reply" AARGH!
 
You may also want to check out TubeCad's Tilt control PCB, which IMO is more suitable for hi-fi use.
 
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